A. Field of the Invention
The embodiments of the present invention relate to an orthopedic blade, and more particularly, the embodiments of the present invention relate to an interchangeable orthopedic blade for more accurately placing in, without excessive damage to, a bone when repairing a fracture in the bone by cooperating with an interchangeable orthopedic plate, so as to provide absolute stable fixation by holding the fracture in its anatomic position and resist applied forces while healing, to thereby provide a stable anatomic restoration and eliminate a need for revision surgery due to failure of fixation or malunion.
B. Description of the Prior Art
(1) General Principles of Internal Fixation.
(a) History of Fracture Treatment.
Fractures have been treated with immobilization, traction, amputation, and internal fixation throughout history. Immobilization by casting, bracing, or splinting a joint above and below the fracture was used for most long bone fractures, with the exception of the femur for which traction was the mainstay of treatment. In the past, open fractures and ballistic wounds with long bone fractures were not amenable to standard fracture care because of the associated soft tissue injury and the difficulty in preventing sepsis. Thus, they usually resulted in amputation, especially during the US Civil War.
Although the concept of internal fixation dates back to the mid 1800s, Lister introduced open reduction and internal fixation (“ORIF”) of patella fractures in the 1860s. Use of plates, screws, and wires was first documented in the 1880s and 1890s. Early surgical fixation initially was complicated by many obstacles, such as infection, poorly conceived implants and techniques, metal allergy, and a limited understanding of the biology and mechanics of fracture healing. During the 1950s, Danis and Muller began to define the principles and techniques of internal fixation. Over the past 40 years, advancements in biological and mechanical science have led to contemporary fixation theories and techniques.
(b) Introduction to Fracture Repair Biology.
Disruption of the endosteal and periosteal blood supply occurs with the initial trauma. Maintaining adequate blood supply to the fracture site is essential for healing. Hunter described the four classic stages of natural bone repair: inflammation; soft callus; hard callus; and remodeling. The inflammation stage begins soon after injury and appears clinically as swelling, pain, erythema, and heat. Disrupted local vascular supply at the injured site creates a hematoma and prompts the migration of inflammatory cells that stimulate angiogenesis and cell proliferation. After the initial inflammatory phase, the soft callus stage begins with an infiltration of fibrous tissue and chondroblasts surrounding the fracture site. The replacement of the hematoma by this structural network adds stability to the fracture site.
Soft callus is then converted into rigid bone, the hard callus stage, by enchondral ossification and intramembranous bone formation. Once the fracture has united, the process of remodeling begins. Fibrous bone is eventually replaced by lamellar bone. Although this process has been called secondary bone union or indirect fracture repair, it is the natural and expected way fractures heal. Fractures with less than an anatomic reduction and less rigid fixation—i.e., those with large gaps and low strain via external fixator, casting, and intramedullary (“IM”) nailing—heal with callous formation or secondary healing with progression through several different tissue types and eventual remodeling. Anatomic reduction and absolute stabilization of a fracture by internal fixation alter the biology of fracture healing by diminishing strain—elongation force—on the healing tissue at the fracture site. Absolute stability with no fracture gap—e.g., via ORIF using interfragmental compression and plating—presents a low strain and results in primary healing—cutting cone—without the production of callus. In this model, cutter heads of the osteons reach the fracture and cross it where bone-to-bone contact exists. This produces union by interdigitation of these newly formed osteons bridging the gap. The small gaps between fragments fill with membranous bone that remodels into cortical bone as long as the strain applied to these tissues does not cause excessive disruption and fibrous tissue develops—nonunion. This method of bone healing is known as direct bone healing or primary bone union. Essentially, the process of bone remodeling allows bone to respond to the stresses to which it is exposed.
Based on the mechanical milieu of the fracture as dictated by the surgeon's choice of internal fixation and the fracture pattern, two patterns of stability can result that determine the type of bone healing that will occur. Absolute stability—i.e., no motion between fracture fragments—results in direct or primary bone healing—remodeling. Relative stability—i.e., a certain amount of fragment motion—heals with secondary or indirect bone union.
(c) Pins and Wires.
Kirschner wires—K-wires, 0.6-3.0 mm—and Steinmann pins—3-6 mm—have a variety of uses from skeletal traction to provisional and definitive fracture fixation. Resistance to bending with wires is minimal so they are usually supplemented with other stabilization methods when used for fracture fixation, but most commonly, wires are utilized as provisional fixation prior to definitive fixation with a stronger device. Skeletal traction with K-wires is possible with the use of a K-wire tensioner that with application stiffens the wire and allows it to resist bending load.
K-wires and Steinmann pins can provide provisional fixation for reconstruction of fractures, while incurring minimal bone and soft tissue damage and leaving room for additional hardware placement. Planning pin placement is important to avoid the eventual permanent fixation devices, and if possible, pins should be placed parallel to screws used for fracture compression. Depending on the diameter, pins may also be used as guidewires for cannulated screw fixation.
Permanent fixation options include fractures in which loading is minimal or protected with other stabilization devices, such as external fixators, plates, and braces. Pin or wire fixation is often used for fractures of the phalanges, metacarpals, metatarsals, proximal humeri, and wrists. K-wires commonly supplement tension-band wire constructs at olecranon, patella, and medial malleolus fractures.
The K-wires can be fully threaded or nonthreaded, and have either diamond or trocar points that are simplistic in design and have limited ability to cut hard bone—a process that can lead to overheating. For this reason, they should be inserted slowly when power equipment is used to avoid thermal necrosis. Image intensifiers are often used for optimal positioning of the fixation, especially with percutaneous insertion combined with closed reduction techniques. The pins may have points at both ends, facilitating antegrade-retrograde fixation techniques. They are, however, a potential hazard and should be used with caution.
Steinmann pins are larger, may be threaded or unthreaded, and are currently used primarily for long bone traction in conjunction with a Bailer traction stirrup. Early techniques of fracture treatment consisting of pins for skeletal traction and incorporation into a cast were fraught with pin infections, loosening, and loss of reduction. This technique has been replaced with more advanced external fixation devices, internal fixation methods, and minimally invasive plating and IM devices.
Guidewires for cannulated screws are employed at times for definitive fixation as they are terminally threaded allowing for fixation on the opposite cortex. An example of this would be the closed reduction and percutaneous pinning technique for proximal humeral fractures.
(d) Screws.
Bone screws are a basic part of modern internal fixation. They can be used independently or in combination with particular types of implants. The common design of a screw consists of a tip, shaft, thread, and head, as shown in FIGS. 1-3. A round screw tip requires pretapping, whereas a fluted screw tip is self-tapping. The screw shaft is located between the head and the threaded portion of the screw. The screw thread is defined by its major or outside thread diameter and minor or root shaft diameters, pitch, lead, and number of threads. The distance between adjacent threads is the pitch.
The lead is the distance a screw advances with a complete turn. Lead is the same as pitch if the screw is single threaded, and lead is twice the pitch if the screw is double threaded—faster screw insertion. The root diameter determines the screw's resistance to breakage—tensile strength. Screws are referred to by their outer thread diameters, bone type for intended use—cortical or cancellous determined by pitch and major/minor diameters—and proportion of thread—partially or fully threaded.
Screw pullout strength can be affected by several factors. Bone composition density—is the primary determinant of screw fixation. The total surface area of thread contact to bone—root area—is another factor in pullout resistance. Pretapping the screw hole theoretically reduces microfracture at the thread-bone interface, but requires an extra step for insertion. Self-tapping screws have been shown to have no clinical difference from pretapped screws for fracture or plate fixation, eliminate the tapping step, and are now the industry standard. The fluted portion of the screw tip has less thread contact with the bone so slight protrusion at the opposite cortex is recommended.
Pitch—the distance between adjacent threads—affects purchase strength in bone. Increasing the pitch increases bone material between the threads, but decreases the number of threads per unit of distance.
The industry standard for the screw head is a hexagonal recess that provides a large contact surface between the screw head and screwdriver and allows for optimal transmission of torque, as shown in FIG. 3. A cross-type screw head is used on some screws in the 2.0 and smaller screw—minifragment—sets. The star design or TORX head found in industry has been adapted to the screw heads for the Association for the Study of Internal Fixation (“AO/ASIF”) locking plates, and has been shown to be superior for torque and resistance to stripping.
Several forces are involved with screw insertion and tightening. Torque is applied through the screwdriver to the screw head in a clockwise rotation to advance the screw in the predrilled path—or in the case of a cannulated screw—over a guidewire. This advancement produces a circumferential force along the thread. For cortical screws, the drill diameter is slightly larger than the root—shaft—diameter of the screw. Axial tension is created with impingement of the screw head on the cortex or plate generating tension through the screw. To optimize these forces, screws should ideally be inserted at 80% of the torque needed to cause them to strip. An estimated 2500-3000 newtons of axial compression force can be applied to the average screw. Over time, the amount of compressive force decreases slowly as the living bone remodels to the stress. The fracture healing time, however, is usually shorter than the time it takes for substantial loss of compression and fixation.
The two basic types of screws available for the variability of bone density are cortical and cancellous screws. Cortical screws are designed for compact diaphyseal bone, whereas cancellous screws are designed for the more trabecular metaphyseal bone. Cortical screws have a smaller major—thread—diameter, decreased pitch, and a shallower thread than cancellous screws. Standard nonlocking cortical screw diameter choices include 1.5, 2.0, 2.7, 3.5, and 4.5 mm.
Cancellous screws typically have a larger major—thread—diameter and pitch and a greater difference between major and minor—shaft—diameters in comparison to cortical screws providing more surface area for bone purchase. These screws are intended for use in metaphyseal fixation where bone is softer. Cancellous screws are available in sizes 4.0 and 6.5 mm, and cannulated sizes vary from 4.0-7.5 mm.
Tapping is not usually necessary in metaphyseal bone, as cancellous bone is porous relative to compact diaphyseal bone and usually requires only the initial pilot hole or cannulated screw guidewire. With subsequent screw insertion, there is compression of the bone along the path of the threads, which increases the local bone density in contact with the thread, thereby potentially increasing screw purchase. Tapping may be considered in strong metaphyseal bone to avoid stripping if advancement of the screw is difficult.
Positional or neutralization screws are to attach an implant, such as a plate, to bone by compression between the plate and bone, as shown in FIG. 4. This function is modified when the screw is used to lag across a fracture through the plate or when used for fracture compression, as with a dynamic compression screw. For a positional screw, the pilot hole is drilled with the appropriate-size bit—shaft diameter—for the screw to be inserted—e.g., a 3.2-mm drill bit for a 4.5-mm screw—using a centering guide for the plate hole. A depth gauge is used to determine appropriate screw length, and the thread cut is then made with an appropriate tap or without a tap when self-tapping screws are used or screws are placed in metaphyseal bone.
Interfragmentary lag screws provide compression across two bone surfaces using the lag technique. A lag screw is a form of static compression, and is applicable to intra-articular fractures to maintain reduction and diaphyseal fractures for stability and alignment. Ideally, lag screw fixation produces maximum interfragmentary compression when the screw is placed perpendicular to the fracture line, as shown in FIGS. 5-7. Most lag fixation techniques require additional stabilization to neutralize the axial bending and rotational forces applied to the bone during functional postoperative care. This is provided by a neutralization or buttress plate or external fixation.
If lag screws are to be used without neutralization plate fixation, especially in long spiral fractures>2 times the diameter of the involved bone—the ideal inclination of the screw is halfway between the perpendiculars to the fracture plane and to the long axis of the bone. Placing the screw perpendicular to the long axis of the bone can also be considered because longitudinal or shear compression may cause the screw or screws to tighten. Interfragmentary screw fixation alone may be appropriate for avulsion injuries in which shear forces generate metaphyseal and epiphyseal intra-articular fractures provided bone quality is good.
A fully threaded screw can serve as a lag screw with the near cortex over-drilled to the size of the screw's major—thread—diameter, 4.5 mm in the example, as shown in FIGS. 8 and 9. Once the near cortex is drilled, which provides a gliding hole, a drill sleeve with the outer diameter of the drill bit—4.5 mm—is inserted into the hole, and the standard drill bit—3.2 mm shaft diameter—is used to drill the far cortex. As the screw threads grasp the distal cortex, compressive forces are generated through the axis of the screw to the screw head causing the fracture fragments to be compressed. This same mechanical effect can be generated by a partially threaded screw, with all threads entirely within the opposite bony fragment.
Cannulated screws are now provided by most trauma manufactures in sizes from minifragment to 7.5 mm usually with a cancellous thread, but cortical patterns are also available as they are more commonly used in periarticular/metaphyseal bone. The guidewire is usually placed under fluoroscopic control, and allows for initial provisional fixation.
Cannulated screws allow for a percutaneous technique, such as is used with hip pinning, or may be used with limited open reduction techniques and can help minimize soft tissue dissection and periosteal stripping. Most designs are now self-drilling and self-tapping, but some may require predrilling over the guidewire with dense bone. The guidewires are usually terminally threaded—although nonthreaded are available—and when drilling over the wire, it is recommended not to drill over the threaded portion because the guidewire may be inadvertently removed along with removal of the drill bit. This could result in difficulty relocating the drill hole through soft tissue or loss of provisional fixation.
The pullout strength of cannulated 7-mm cancellous screws versus 7-mm noncannulated screws and 3.5-mm cannulated and noncannulated screws has been tested in two studies, and no significant difference was noted regarding pullout strength. These studies, however, are specific to these screw designs and similar fixation properties cannot necessarily be applied to other screw designs and sizes. It should also be considered that the relative costs of cannulated screws are often ten times that of similar-sized noncannulated screws. Therefore, noncannulated screws should be used when technically feasible.
Self-tapping screws have the advantage of eliminating a step during screw insertion, thereby decreasing operative time. The fluted design of the screw cuts a sharp path in the predrilled hole eliminating the need for tapping. Baumgart and associates showed that insertion torque and pullout strength were comparable for tapped and self-tapping screws. Only if the cutting tip did not protrude through the second cortex did they find a reduction of pullout strength of approximately 10%.
Schatzker and associates went on to prove that self-tapping screws inserted at 80% of thread-stripping torque, and then removed and reinserted twelve times did not lose any significant holding power. When inserting a self-tapping screw as a lag screw, care should be taken with technique to avoid missing the opposite cortex as these screws are often at an angle to the diaphyseal shaft or there may be difficulties with advancing the screw while also tapping, especially with hard cortical bone. It is not unreasonable to consider tapping this opposite cortex first to help with alignment and advancement of the lag screw.
Locked screws are incorporated in more recent plate designs, and may be inserted as unicortical or bi-cortical screws depending on the type of plate and fracture. These screws—with reduced pitch—produce minimal axial force—if any—and provide biomechanical fixation by locking the screw head into the plate with a tapered thread perpendicular to the plate. Some newer designs allow for some variable angulation of the locking screws. The system acts generally like an internal-external fixator, as shown in FIGS. 10 and 11. These systems are discussed further in Plates below.
(e) Plate Types.
Plates are provided in various sizes and shapes for different bones and locations. Dynamic compression plates (“DCPs”) are available in 3.5 mm and 4.5 mm sizes. The screw holes in a DCP are shaped with an angle of inclination on one side away from the center of the plate. When tightened, the screw head slides down the inclination causing movement of the bone fragment relative to the plate, as shown in FIG. 12. As one bone fragment approaches the other at the fracture, compression occurs. The shape of the holes in the plate allow for 25° of inclination in the longitudinal plane and 7° inclination in the transverse plane for screw insertion.
The dynamic compression principle requires that the holes of the plate be shaped like an inclined and transverse cylinder. Like a ball, the screw head slides down the inclined cylinder. Because the screw head is fixed to the bone via the shaft, it can only move vertically relative to the bone. The horizontal movement of the head as it impacts the angled side of the hole, results in movement of the bone fragment relative to the plate, and leads to compression of the fracture.
Limited-contact DCPs (“LC-DCPs”) were designed to limit possible stress shielding and vascular compromise by decreasing plate-to-bone contact by 50%, as shown in FIG. 13.
Theoretically, this leads to improved cortical perfusion with increased preservation of the periosteal vascular network, and reduces osteoporosis under the plate. The regular DCP has an area of decreased stiffness located at the plate holes, and with bending, has a tendency to bend at the holes with a segmented pattern, whereas the LC-DCP—with a different geometric design incorporating the holes and plate undersurface—allows for gentle bending distributed throughout the plate, as shown in FIGS. 14A and 14B.
Finally, the LC-DCP is designed with plate hole symmetry providing the option of dynamic compression from either side of the hole, and allowing compression at several levels. In general, standard DCP style plates were replaced years ago with updated designs by most manufacturers with variations on the LC-DCPs, and in turn, these plates have been replaced by all manufacturers with plates capable of both locking and nonlocking functions. Some specific non-locking-style plates are still retained in use as they function well for a variety of specific fractures, such as the one-third tubular plate for lateral malleolar fractures and the 3.5 mm recon plates for periacetabular fixation.
Techniques for the application of both the DCP and LC-DCP are the same, as shown in FIG. 15. Screws can be inserted in neutral position or a compression position depending on the desired mechanical result. The DCP uses a green guide to insert a neutral screw, which adds some compression to the fracture owing to the 0.1-mm offset. The gold guide produces a hole 1 mm off-center, away from the fracture, and allows for 1 mm of compression at the fracture site with tightening of the screw. The LC-DCP universal drill guide allows for either neutral or eccentric placement of screws. When creating an eccentric hole to one side or another, the guide is slid to the end of the plate hole without applying pressure, and the hole is drilled. By placing pressure against the bone with the drill guide, the spring-loaded mechanism allows for centralization of the hole for neutral screws—particularly if the screw must be inserted at an angle to the plate.
The 3.5 one-third tubular plate is 1 mm thick and allows for limited stability, as shown in FIG. 16. The thin design allows for easy 2-dimensional contouring and is primarily used on the lateral malleolus, and on occasion, the distal ulna. The oval holes allow for limited fracture compression with eccentric screw placement.
Improvements by all manufacturers have been made for plates used for almost all areas of the body that require placement of a plate near a joint and over extended areas of diaphyseal bone. The refinement of contour—along with screw head modification reduces hardware prominence and increases fixation options.
The 95°-angled plates are useful in the repair of metaphyseal fractures and reconstruction of the femur as they provide very rigid fixation, as shown in FIGS. 17A-17D. They are technically demanding, and proper insertion requires the blade to be inserted with consideration of 3 dimensions—i.e., vagus/valgus angulation, anterior/posterior position, and flexion/extension rotation of plate. The screw barrel devices are considered somewhat easier to insert because the flexion/extension of the plate is correctable after insertion of the screw.
Reconstruction plates are thicker than one-third tubular plates, but they are not quite as thick as DCPs, as shown in FIGS. 18A and 18B. Designed with deep notches between the holes, they can be contoured in three planes to fit complex surfaces—e.g., around the pelvis and acetabulum. Reconstruction plates are provided in straight and slightly thicker and stiffer precurved lengths. As with tubular plates, they have oval screw holes allowing potential for limited compression.
Cable plates incorporate a large fragment plate with cerclage wires to be used with a tensioning device. These are used primarily with femoral fractures surrounding or adjacent to prosthetics—femoral hip or knee implants. Cortical allograft struts are often incorporated for osteoporotic bone.
(f) Plate Functions.
Standard plate fixation requires exposure of the fracture site, hematoma evacuation, and reduction of the fracture with possible interfragmentary lag fixation. After a fracture occurs, the periosteal blood supply is dominant, and this network of connective tissue must be preserved to optimize healing. Excessive periosteal stripping and careless soft tissue techniques can impair local blood supply and prolong healing.
Diaphyseal plate fixation associated with an anatomic reduction and interfragmentary compression provides absolute stability. Plates are often indicated in articular fractures to neutralize the axial forces on the interfragmentary screws compressing cancellous bone to facilitate its healing. A fracture anatomically reduced without a gap and fixed with absolute stable fixation will undergo primary healing.
Dead bone at the fracture site is resorbed by osteoclasts of the cutting cones as these cells traverse the fracture site. The osteoclasts are closely followed by ingrowth of blood vessels and mesenchymal cells and osteoblast infiltration. Stress shielding of the bone is rarely caused by the plate relieving axial load to the bone. Plate-induced osteoporosis is caused by disruption of the local vascularity to the bone cortex secondary to an impediment of centrifugal cortical blood flow by the plate.
Osteoporosis under a plate should be kept in mind after removal of hardware because the bone also has the mechanical disadvantage of empty screw holes. This vascular-caused cancellization of the cortical bone in diaphyseal areas usually resolves within two years of plate application so it is safe to remove a plate at this time with the refracture rate being minimal. Plates applied to metaphyseal areas may have the option of earlier removal depending on the amount of diaphyseal extension and healing.
Bridge plating is used for comminuted unstable fractures in which anatomic restoration and absolute stability cannot be achieved. Minimal exposure and indirect reduction techniques are used to preserve the blood supply to the fracture fragments for healing, and a plate is attached to the two main fragments spanning the area of fracture. The plate is used to provide proper length, axial alignment, and rotation, but it is obviously limited for any load.
With more recent advances of combining minimally invasive plate techniques utilizing locking plate technology, plate devices act more as an internal fixator. This approach began in 2001 with the Less Invasive Surgical Stabilization (“LISS”) plate that is advanced in the submuscular tissue through a small incision over the periosteum, but does not necessarily contact the bone along the length of the plate. This technique limits the disruption of periosteal blood supply that is seen in conventional plating systems as the fixation is through the locking screws, thereby not necessitating compression to the plate for stability. The early development of this concept with the Point Contact Fixator (“PC-Fix”) system in the 1990s—and then later with LISS—takes advantage of unicortical, self-drilling, and self-tapping screws with threaded screw heads that lock into the screw hole of the plate and minimize soft tissue disruption.
Once the LISS plate is aligned with the central shaft of the bone, screw placement can be accomplished percutaneously with a radiolucent guide attachment to the plate. Unicortical screws are recommended for use in diaphyseal bone, with longer screws for use in the metaphyseal area, thereby functioning as a fixed-angle device.
Currently, most manufacturers offer new locking plate products. These devices range from standard straight plates of all sizes with locking and standard screws to anatomically specific plates that act as fixed-angle devices. These new plate designs incorporate improved contour with locking screw options for fixation offering significant advantages over the conventional designs for certain fractures. Proximal and distal humerus, distal radius, distal femoral, and proximal—bicondylar—and distal tibial fractures are examples of injuries that benefit from this technology having the improved ability to hold a fracture in its anatomic position and resist applied forces while healing. Conventional plates—that rely on friction forces against the plate from screw fixation and buttressing in metaphyseal and articular fractures—are limited in resisting applied loads versus locking fixation.
In contrast, certain shaft fractures with stable patterns and adequate room for fixation have proven high union rates with conventional plating—humeral shaft, radius, and ulna shaft—and any significant difference between the two techniques is difficult to realize with proper surgical technique. Current recommendations are to use locking screws in situations with limited fixation options, osteoporotic bone, or need for fixed-angle support. For example, a simple lateral plateau fracture that requires buttress fixation and with which the bone quality is reasonable can be adequately treated with a conventional nonlocking lateral plate.
Currently, most LC-DCP small and large conventional plate sets have been reduced as utilization of specialty plates has increased with periarticular design and locking capability, the surgeon deciding which screws are locking or nonlocking depending on the fracture. As with cannulated screws, locking screws can vary in cost ranging from 8-15 times the cost of a conventional screw, and therefore should be used when needed based on the fracture pattern and expected loads. This cost issue is lessened to some degree when taking into account the need for revision surgery due to failure of fixation or malunion. Thus, a balance of usage guided by conventional wisdom, common sense, and biomechanical and outcome studies is recommended.
(g) Tension-Band Principle.
Plates and other constructs can be used to function as a tension-band if an eccentrically loaded bone—e.g., the femur—has the device placed on the tension-convex side of the bone. Using load-strain diagrams, Frederic Pauwels—who first described the tension-band concept—showed that a curved tubular structure placed under an axial load had a tension side and a compression side. With this theory, he described the application of internal fixation on the tension side to convert tensile forces into compressive forces at the fracture site.
With static compression applied by the implant—e.g., tensioning of wire compression with plate—dynamic compression then develops with joint flexion as with a patella or olecranon fracture or with load as with lateral femoral plating, as shown in FIGS. 19A and 19B. With this technique, the internal fixation device must have the strength to withstand the tensile distraction forces created by muscles during motion, and the bone on the opposite side of the plate must be able to withstand the compressive forces as a medial buttress.
Wires and plates are usually quite strong under pure tension forces, but with bending forces added fatigue can occur rapidly. If bony support is compromised on the cortex, opposite from the tension device—e.g., from fragmentation, osteoporosis—bending stresses can develop causing failure of fixation. Wiring techniques commonly include longitudinal K-wires for rotational and axial alignment control in the case of bone fragmentation.
Conversely, fixation on the concave side of the bone occurs in rare situations, such as with medial plating of a femur or anterior plating of the humerus. In these situations, fractures have minimal resistance to bending stresses, and gapping can occur on the convex side resulting in failure of fixation, as shown in FIG. 20. Therefore, attempts should be made to limit potential bending forces to fixation to prevent fixation failure. The tension-band principle can be applied to wires, cables, sutures, plates, and external fixators as long as the basic principles are followed.
(2) Angled Plates.
(a) General Principles.
In 1959, the AO developed the angled plates, as shown in FIGS. 21 and 22. The “U” profile was chosen for the blade portion, and a single blade unit with a fixed angle between the blade and the plate was adopted in preference to the two-piece variable angle devices. The advantage of the fixed angle is the increased strength and the increased corrosion resistance of the implant. The disadvantage is the increased difficulty of insertion. In the proximal femur, the blade has to be inserted in the middle of the femoral neck and at a predetermined angle to the shaft axis. In addition, the plate portion of the angled blade plate has to be inserted so that it will line up with the axis of the shaft at the end of the procedure. In the distal femur, the blade has to line up with the joint axis and with the inclination of the patellofemoral joint and be inserted exactly into the middle of the anterior half of the femoral condyles at a predetermined distance from the joint, and the plate has to line up with the axis of the femoral shaft. Because of these technical complexities, a preoperative plan—including a preoperative drawing—is essential so that the operation can follow it step-by-step. The surgeon must also exercise great care at the time of surgery and pay particular attention to anatomic landmarks, position, and inclination of the implants in order to follow the preoperative plan. This usually ensures that at the end of the procedure, everything fits and that the desired end result is achieved.
(b) Preoperative Planning
An X-ray of the normal side is required in order to have a template on which to plan the procedure. For the proximal femur, the X-ray must be taken with the hip in 15°-20° internal rotation to correct for ante-version. For the distal femur, accurate antero-posterior and lateral X-rays centered on the joint are necessary. The outlines of the proximal or the distal femur are drawn in, as are all the fracture lines. The fracture pattern determines the steps of the internal fixation, as well as the choice of plate. The selected plate is drawn in with the help of the templates. The plan should include the order in which the different steps will be carried out, should denote the function of the different screws, should indicate if a gliding hole or a thread hole needs to be predrilled before the reduction is carried out, and whether a bone graft is necessary. All the guide wires that are necessary to execute the procedure must also be shown, and their function and inclination carefully noted Schatzker rationale.
These working drawings are necessary before any surgical procedure is embarked upon. They are of particular importance before corrective osteotomies because they are the only way the surgeon can check preoperatively the result of the osteotomy, as well as the three-dimensional concept of the procedure.
(c) Implants and Instruments.
A number of specialized instruments have been developed that greatly facilitate the exact execution of the operation in accordance with the preoperative plan. Neither an X-ray nor an image intensifier is a substitute for a three-dimensional concept of the local anatomy, nor will they serve as a guide to the correct insertion of the guide wires. Correct insertion is based on the anatomic landmarks and on the particular device employed for fixation. The X-ray or the image intensifier are, however, useful to verify the definitive insertion of the seating chisel or of the specialized guide wire for the dynamic hip or condylar screw. An X-ray is also useful as a permanent intra-operative record of the position of the guide wires and of all the internal devices, as well as of the position of an osteotomy if one is being carried out.
(d) The Angled Plates for the Proximal and Distal Femur.
Initially, as shown in FIG. 21, the AO developed the 130° plate for use in the proximal femur, and, as shown in FIG. 22, the condylar blade plate is for use in the distal femur. With time it became evident that the condylar plate could also be used for the treatment of certain inter-rochanteric and subtrochanteric fractures of the proximal femur. Following further modifications and refinements, the AO has developed the dynamic hip screw (“DHS”) and the dynamic condylar screw (“DCS”). These two have almost replaced the “U” profile angled blade plates in the treatment of fractures, but the latter continue to be used in reconstructive surgery, such as osteotomies. The original fixed angle devices are described in detail because all the specific features, indications, and anatomic considerations apply in exactly the same way as to the DHS and to the DCS.
The 130° angled plate has a blade with a “U” profile, as shown in FIG. 21. The plate portion comes in varying lengths depending on the particular fracture to be fixed. Thus, the four- or six-hole plates are used for most intertrochanteric fractures, and the plates—9-12 holes—for subtrochanteric fractures.
The condylar plate has a fixed angle of 95° between its blade and plate portion, as shown in FIG. 22. The shortest plate available has five holes. The length to be used will vary with the fracture pattern. The shortest blade is 50 cm, and the length of the blade chosen will depend on the size of the femur and whether the plate is being used in the distal or proximal femur.
Numerous innovations for osteosynthetic devices have been provided in the prior art, which will be described below in chronological order to show advancement in the art, and which are incorporated entirely herein by reference thereto. Even though these innovations may be suitable for the specific individual purposes to which they address, nevertheless, they differ from the embodiments of the present invention in that they do not teach an interchangeable orthopedic blade for more accurately placing in, without excessive damage to, a bone when repairing a fracture in the bone by cooperating with interchangeable orthopedic plate, so as to provide absolute stable fixation by holding the fracture in its anatomic position and resist applied forces while healing, to thereby provide a stable anatomic restoration and eliminate a need for revision surgery due to failure of fixation or malunion.
(1) U.S. Pat. No. 4,711,232 to Fischer et al.
U.S. Pat. No. 4,711,232—issued to Fischer et al. on Dec. 8, 1987 in U.S. class 606 and subclass 67—teaches a fastener for anchoring in a bore in a bone, which has a screw with a substantially cylindrical outer surface formed with a helical screw thread. The screw has at its screw thread, a thread diameter, and between the turns of the thread at the surface, a root diameter smaller than the thread diameter. A synthetic-resin anchor sleeve of a resilient fitted in the bore is of an outside diameter corresponding generally to the diameter of the bore, and has an outer end formed with an outwardly open polygonal-section recess, an inner end formed with an inwardly open and transversely through-going slot, an outer end portion of an inside diameter greater than the root diameter but smaller than the thread diameter, an inner end portion of an inside diameter smaller than the root diameter, and an external helicoidal screw thread extending about two-thirds of the length of the sleeve from its inner end toward its outer end.
(2) U.S. Pat. No. 5,098,434 to Serbousek.
U.S. Pat. No. 5,098,434—issued to Serbousek on Mar. 24, 1992 in U.S. class 606 and subclass 308—teaches a bone screw for joining bone fragments or for mounting a prosthetic component onto an underlying bone. The bone screw includes a head and an elongated cylindrical shank that is integral with, and extends from, the head. The shank includes a threaded member and a shoulder member connecting the threaded member and the head. The shoulder member has an outer surface with a porous medium thereon for encouraging bone ingrowth fixation. The outer diameter of the shoulder member is greater than the diameter of a bore of the bone into which the screw is to be threadedly engaged. The head of the screw is provided with a coupling member engageable by a tool for selectively rotating the shank to advance the screw into the bone. As the bone screw is advanced toward a fully seated position, the shoulder member with the porous medium thereon engages the bone in a fitting manner that is described as a “scratch fit.” Initial loosening of the bone screw due to the viscoelastic relaxation of the bone tissue following fixation is thereby largely inhibited and long term loosening of the bone screw is also inhibited by providing an interface onto which, or into which, bone tissue can grow to stabilize the repair site or the implanted component.
(3) U.S. Pat. No. 5,899,906 to Schenk.
U.S. Pat. No. 5,899,906—issued to Schenk on May 4, 1999 in U.S. class 606 and subclass 301—teaches a threaded washer having a central bore for use with a bone screw. The washer is threaded into a counterbore extending below the bone surface and into cancellous bone material. The external washer threads are tapered. The bone screw is inserted through the central bore of the washer and threaded into the fragment beyond the fracture. The washer permits the bone screw head to be located beneath the bone surface.
(4) U.S. Pat. No. 5,997,541 to Schenk.
U.S. Pat. No. 5,997,541—issued to Schenk on Dec. 7, 1999 in U.S. class 606 and subclass 303—teaches a threaded washer having a central bore for use with a bone screw. The washer is threaded into a counterbore extending below the bone surface and into cancellous bone material. The external washer threads are tapered. The bone screw is inserted through the central bore of the washer and threaded into the fragment beyond the fracture. The washer permits the bone screw head to be located beneath the bone surface.
(5) U.S. Pat. No. 6,048,344 to Schenk.
U.S. Pat. No. 6,048,344—issued to Schenk on Apr. 11, 2000 in U.S. class 606 and subclass 916—teaches a threaded washer having a central bore for use with a bone screw. The washer is threaded into a counterbore extending below the bone surface and into cancellous bone material. The external washer threads are tapered. The bone screw is inserted through the central bore of the washer and threaded into the fragment beyond the fracture. The washer permits the bone screw head to be located beneath the bone surface.
(6) United States Patent Application Publication Number 2010/0331895 to Linke.
United States Patent Application Publication Number 2010/0331895—published to Linke on Dec. 30, 2010 in U.S. class 606 and subclass 304—teaches an osteosynthetic device for the fixation of a bone or bone fragments, which has a longitudinal axis, and includes a bone screw with a shaft bearing a thread, a front end, and a rear end. The thread has a maximum outer diameter, and a wing-like blade with a leading end being connected to the front end of the bone screw and a trailing end being connected to the rear end of the bone screw. The blade is further provided with a coaxial longitudinal aperture having a length extending between the leading end and the trailing end, and a width. Further, the blade is coaxially and rotatably mounted on the shaft of the bone screw.
(7) United States Patent Application Publication Number 2010/0312245 to Tipirneni et al.
United States Patent Application Publication Number 2010/0312245—published to Tipirneni et al. on Dec. 9, 2010 in U.S. class 606 and subclass 62—teaches a bone screw including a sleeve, a shaft reciprocally received within the sleeve, and a compressive device. The bone screw may be extended—placing a fracture in tension—after insertion into a bone, and then retained in place by a setscrew that is retained by an intramedullary rod. The shaft of the bone screw has a blade thread that allows the bone screw to be installed into a bone by tapping the bone screw with a hammer.
It is apparent that numerous innovations for osteosynthetic devices have been provided in the prior art, which are adapted to be used. Furthermore, even though these innovations may be suitable for the specific individual purposes to which they address, nevertheless, they would not be suitable for the purposes of the embodiments of the present invention as heretofore described, namely, an interchangeable orthopedic blade for more accurately placing in, without excessive damage to, a bone when repairing a fracture in the bone by cooperating with an interchangeable orthopedic plate, so as to provide absolute stable fixation by holding the fracture in its anatomic position and resist applied forces while healing, to thereby provide a stable anatomic restoration and eliminate a need for revision surgery due to failure of fixation or malunion.